Subsea production systems typically include a christmas tree or similar apparatus which is mounted at the upper end of a well bore that extends into a subterranean hydrocarbon-bearing formation. The principal function of the christmas tree is to provide an interface between the well and the external environment for regulating the flow of production fluid from the well and for facilitating intervention on the well or downhole systems during the operational life of the well. Accordingly, christmas trees commonly include a number of flow control valves and associated actuators for controlling the flow of production fluid from the well, as well as multiple sensors for monitoring certain operating conditions of the production system, such as the state of the valves and actuators and the properties of the production fluid.
Similarly, subsea processing systems usually comprise flow control valves and associated actuators for regulating the flow of production fluid through a processing apparatus. In addition, these systems commonly employ a number of sensors for monitoring certain operating conditions of the system, such as the state of the various components of the apparatus and the properties of the production fluid.
The various components of subsea production and processing systems are controlled and/or monitored by a subsea control module (SCM) which in turn is monitored and/or controlled by a remote monitoring and control station. The SCM is normally located on or adjacent the subsea production or processing apparatus, and the monitoring and control station is typically located on a surface vessel or platform or at a remote land-based facility. The SCM is usually connected to the monitoring and control station through an umbilical. The umbilical may include hydraulic lines for supplying hydraulic fluid to various hydraulic actuators located on he subsea production or processing apparatus. The umbilical may also include electric and/or fiber optic lines for supplying electrical power to certain components of the production and processing system and for communicating control signals and data between the monitoring and control station and the SCM.
Conventional subsea production and processing systems incorporate a relatively small number of sensors to measure the operating conditions of the system. In order to maximize production efficiency it is necessary to optimize the functioning of the subsea production or processing system. A key component in such optimization is the effective monitoring of the system using a range of sensors. To do this effectively requires employing far more sensors on the system than are conventionally used.
In addition to the sensors, means for relaying the sensor outputs to the SCM are also required. The sensors on subsea production and processing systems are conventionally hardwired to the SCM using electrical or optical fiber cabling. The requirement for such cabling and their connections into the sensors and the SCM constitute a significant cost and technical challenge. Further, when the number of sensors is greatly increased, the cabling and connections become a major limitation. Moreover, employing a large number of sensors and associated cabling under the insulation layer on, for example, a christmas tree is restricted by the potential for the cables to damage or degrade the insulation.
Conventionally acoustic techniques have been employed for underwater wireless communication. However, such systems have low data capacity and are limited by background noise and noise from subsea devices. In addition, acoustic communications are adversely affected by ambient conditions, such as temperature gradients and air bubbles. Acoustic systems are thus not a viable option for wirelessly connecting multiple sensors to an SCM in a subsea production or processing system.
Thus, there exists a need for an efficient and effective means for wirelessly connecting numerous sensors on a subsea production or processing apparatus to an SCM to enable the SCM and/or a remote monitoring and control station to monitor the operating conditions of the production or processing system and control various components of the system.